Light modulating cell



Nov. 30, 1937. s. L. CLOTHIER ET AL LIGHT MODULATING CELL Filed June 4, 1936 zs oPiac Patented Nov. 30, 1937 UNITED STATES Search Room PATENT OFFICE LIGHT MODULATIN G CELL Stewart L. Clothier, Hasbrouck Heights, and

Harold C. Hogencamp, Fairlawn, N. J., assignors to Kolorama Laboratories, Inc., Newark, N. J a corporation of New Jersey Application June 4, 1936, Serial No. 83,588

13 Claims.

This invention is a light modulating cell capable of exhibiting the Kerr effect upon a beam of polarized light. More particularly, the invention comprehends a cell of the type indicated designed for use in a circular polariscope, and it has an internal capacity such that it is admirably adapted for use in high definition television systems.

At the present time there are available many modified forms of the original Kerr cell, but these, so far as they are known to us, are all deficient in one respect or another for high definition television systems, particularly because of the relatively high internal capacity of the cells which makes them impractical for use in television systems wherein pictures of an order of 200 lines are transmitted. An example of a well known type of modified Kerr cell is the multiple plate cell of Dr. Karolus which, due to its high internal capacity, is practically useless in a television system wherein pictures of more than 60 lines are transmitted. The high electrostatic capacity of multi-plate cells of this type introduces such high losses in high definition systems as to render them prohibitive in this particular field.

The disadvantages accruing from high, inherent, electrostatic capacity of cells of the type just referred to have been somewhat remedied by certain low capacity types of cell such as the Wright cell, but both the Wright type cell and the Karolus type cell are designed for use in connection with linear polariscopes wherein substantially only one-half of the light entering the polariscope is utilized.

With the foregoing facts in mind the present invention contemplates a cell capable of exhibiting the Kerr effect on a beam of polarized light which cell has an extremely low, almost negligible inherent electrostatic capacity and which may be employed in a circular polariscope. Thus the cell of the present invention is admirably adapted for use in connection with high definition television systems in that its losses, due to capacitance, are negligible, and due to its ability to pass a circularly polarized beam of light, it utilizes substantially the full light entering the polariscope.

A preferred embodiment of the invention is fully described in the following specification and illustrated in the accompanying drawing, the novel features of the cell being pointed out more particularly in the appended claims.

Figure 1 is a longitudinal sectional view of the cell.

Fig. 2 is a transverse sectional view taken on the line 2-2 of Fig. 1.

Fig. 3 is a transverse sectional view taken on the line 3-3 of Fig. 1.

Fig. 4 is a diagrammatic view illustrating the manner in which the cell of this invention is embodied in a circular polariscope for use in connection with high definition television systems. Figs. 5 and 6 are diagrammatic views showing modified forms of electrode structure.

Referring more particularly to the accompanying drawing, wherein like reference numerals are used to designate like parts throughout, I repre-- sents a hollow, tubular casing member of insulating material such as glass, the same being here shown circular in cross-section, but which may have any convenient or desired cross-sectional form. The casing I is provided with end closure members 2 which are of glass or similar transparent material and which are secured to the respective ends of the casing member I by suitable cap or ring members 3, 3 in a manner to obtain a liquid-tight joint between said closure plates and the respective end portions of the casing I. If desired the joints 4 may be ground or provided with any suitable sealing compound to insure a liquid-tight joint at this point.

Mounted within the casing I is an elongated hollow electrode 5, said electrode being maintained in spaced relation with the inner walls of the casing I by means of spacing disks 6, the latter being provided with a plurality of perforations I to permit free circulation of the birefringent fluid 8 which substantially fills the casing I and maintains electrode 5 completely submerged. The electrode 5 is preferably disposed centrally of the casing I with its longitudinal axis coincident with the axis of the casing and/or the transparent closure members 2, 2. The electrode 5 is provided with a conical bore 9 at each end and extending longitudinally of said electrode with the axes of said cones aligned and coinciding with the axis of the electrode. As shown clearly in Fig. 1, the conical bores 9, 9 are oppositely disposed and extend from the respective ends of the electrode inwardly towards each other,

the apices of the cones meeting at a point In substantially midway between the ends of the cone. Thus the walls of the conical bores 9, 9 converge from the respective ends of the electrode longitudinally along the axis of the electrode to the point l at which a small aperture of the order of 1 mm. is provided.

A second electrode l I in the form of a filament or strand of wire or other metallic structure is mounted to extend longitudinally within the electrode coaxially thereof and coaxially of the conical bores 9, 9. As shown in Fig. l, the electrode II is mounted upon suitable electrode supports I2, I2 which extend radially of the casing I and pass through said casing to provide exterior connection portions I3. Where the electrode supports I2 pass through the casing wall I they may be suitably sealed at II as by fusing the material of the casing at this point or providing the same with a suitable sealing compound. The electrode I I is preferably maintained under a slight degree of tension so as to maintain proper spacing of the electrodes 5 and l l at the point of restriction It], as shown in Fig. 1. In assembly the electrode II which is preferably of fine tungsten wire, is spot-welded to one of the supports l2 and then, while a slight degree of tension is maintained thereon, it is spot-welded to the other electrode support [2. The electrode supports I2 may preferably be made of nickel or tungsten and the electrode 5 is preferably made of nickel and is provided with a connection I5 which extends exteriorly of the casing I, said connection being suitably sealed as at l6 where same passes through the casing wall I.

The casing I may be provided with any suitable means, not shown, for filling the interior of the casing with a suitable birefringent fluid such as nitro-benzene or the like. Thus, the casing may be provided with a suitable filling means or spout which may be sealed ofi when the container is initially filled.

In Fig. 4 there is diagrammatically shown a circular polariscope employing the cell of the present invention and in this figure, 20 represents a calcite block, 2| a one-quarter wave plate of mica or similar birefringent material, and 22 a condensing lens. The elements just mentioned are interposed between a light source 23 and the cell of the present invention which is here diagrammatically shown and indicated by the reference character C. The usual apertured plate is shown at 24 and between the plate 24 and the cell 3 are arranged a second lens 25, a second onequarter wave plate 26 and a block of calcite 21. The electrodes of the cell are placed under suitable potential bias by means of the battery B or its equivalent, and when the apparatus is designed for use in reception of pictures, signals or the like, the signal energy is superposed upon the battery circuit in any conventional manner such as by electrostatic or inductive coupling. As is well understood in the art, variations in the signal or picture energy are reproduced in light intensities at the aperture of the plate 24.

The optical system shown in Fig. 4 may be conveniently assembled in unitary form as indicated by the dotted tubular casing 30, if desired. This not only facilitates handling and placing of the apparatus, but also insures a proper spacing of the lens elements 22 and 25 with reference to the point IU of the cell. The point of maximum construction of the bore of the electrode 5 is placed coincident with the focal points of the lenses 22 and 25 and in order to operate the cell with a maximum degree of light efliciency, the conical walls of the bores 9, 9 are arranged to conform substantially to the cones of light defined by the lenses 22 and 25.

From the foregoing description it is apparent that due to the novel manner in which the electrodes in our cell are constructed, the internal capacity thereof has been kept very low, ahnost negligible. This is due primarily to the filamentary form of one of the electrodes. The novel manner in which the electrodes are disposed permits cutting down materially on the distance or space between the electrodes, while at the same time, for any given effective light opening, the capacity of the cell is greatly reduced without reducing its rotating ability or retardation. The importance of this spacing of, the electrodes is recognized at once when the following formula is considered and wherein K represents a suitable constant, L the length of the electrodes, E the applied voltage and D the distance between the electrodes:

In the present construction of cell the distance between the electrodes is the mean radius of the conical bores 9, 9, and this may be kept quite low due to the simple construction of the cell, and this feature, when considered in connection with the low capacity of the cell due to the filamentary form of the electrode 1 l, makes the cell admirable for use in high definition television systems. Completely successful and highly economical operation of the cell has been carried out in systems transmitting 200 line pictures at the rate of 24 pictures per second, and indications are that the cell is capable of functioning under much higher definition and resulting frequencies.

It is to be understood that the above described conical bores 9 of the electrode 5 are not truly conical in a technical sense but are rather frustroconical by reason of the fact that the bores intersect on a common plane substantially perpendicular to the axes of the bore, said plane cutting the walls of the bore at the point designated by the reference character Hi. It might be stated, however, that inasmuch as the aperture at the point I is of the order of 1 mm. in diameter, the recesses defining the bore are substantially conical.

Furthermore, it is to be understood that the term point" as applied to that portion of the bore designated by the reference character I0, is not used in a geometric sense as defining the intersection of two lines, but rather in the sense of denoting position, location or place.

It is to be understood that by the terms birefringent flui and birefringent medium as used throughout the specification and claims, is meant a medium or fluid which is of itself birefringent or which becomes birefringent when placed under electrical stress as by an electrical potential bias placed across electrodes immersed in such fluid or medium.

It is to be further understood that the preferred embodiment of the invention illustrated in the accompanying drawing and described in the foregoing specification is not to be understood as limiting the invention to the particular modification disclosed but that various changes in relation, size and disposition of the parts may be made as clearly fall within the scope of the appended claims without departing from the spirit of the invention. Thus, for example, the electrode might be made with a substantially cylindrical bore with the electrode ll disposed coaxially thereof such as shown in Fig. 5 of the drawing. Also, a pair of needle pointed electrodes might be substituted for the filament or strand electrode II in which event the needle points would be slightly separated at the point l0 and the external connections 13 connected together as shown in Fig. 6 of the drawing.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A light modulating cell comprising a body of birefringent fluid, an elongated hollow electrode immersed in said fluid, a filament electrode extending coaxially within said hollow electrode and separated from the hollow electrode by said birefringent fluid, and means for passing a beam of light longitudinally through said hollow electrode.

2. A light modulating cell comprising a body Rotation 38. Ulllcs of birefringent fluid, an elongated filamentary electrode immersed in said fluid, a. hollow electrode surrounding said filamentary electrode in spaced relation, the inner wall surface of said hollow electrode diverging from a position intermediate the ends of said electrode toward opposite ends thereof, and means for passing a beam of light longitudinally through said hollow electrode.

3. A light modulating cell comprising a body of birefringent fluid, an elongated filamentary electrode immersed in said fluid, a hollow electrode surrounding said filamentary electrode in spaced relation, said hollow electrode being provided with opposed substantially frustro-conical bores, the walls of which converge from the opposite ends of the electrode toward an intermediate portion of the electrode, and means for passing the beam of light longitudinally through said bores.

4. A light modulating cell comprising a body of birefringent fluid, an elongated filamentary electrode immersed in said fluid, a hollow electrode surrounding said filamentary electrode in spaced relation, said hollow electrode being provided with opposed substantially frustro-conical bores arranged with their bases adjacent to the ends of the electrode and cut by a common plane of intersection adjacent their apices located substantially midway between the ends of said electrode, and means for passing a beam of light longitudinally through said hollow electrode.

5. A light modulating cell comprising a body of birefringent fluid and a pair of electrodes immersed therein, one of the said electrodes comprising an elongated conducting body provided at each end with a longitudinally extending, substantially frustro-conical bore, the wallsof said bores converging from each end of the electrode to a portion of the electrode positioned substantially midway between the ends thereof, the other of said electrodes comprising a conducting strand positioned coaxially of the first-mentioned electrode and extending longitudinally therethrough, and means for passing a beam of light through said bores.

6. A light modulating cell comprising a container, a body of birefringent fluid contained therein, said container including aligned transparent windows in the spaced walls of the container, an elongated hollow electrode mounted within said container in axial alignment with said windows, a second electrode positioned coaxially of the hollow electrode and spaced from the inner wall surfaces thereof, the space between said electrodes being occupied by said birefringent fluid, and circuit connection means for said electrodes extending exteriorly of the container.

'7. A light modulating cell comprising means defining a light path, a pair of electrodes mounted within said path, one of said electrodes comprising an elongated conducting body having a longitudinal bore extending therethrough and aligned with said first mentioned means, the other of said electrodes comprising a conducting strand extending coaxially within the first-mentioned electrode in spaced relation with respect thereto, and a birefringent fluid surrounding said electrodes and filling the space therebetween.

8. A light modulating cell comprising a container and means for defining a path for a beam of light therethrough, a pair of electrodes mounted within said container, one of said electrodes L-UGI cu nuum comprising an elongated hollow conducting member provided with a substantially frustro-conical bore at either end thereof, the conical walls of said bores converging from the opposite ends of said electrode towards a common plane of intersection located substantially midway between the ends of said electrode, the other of said electrodes comprising a conducting strand mounted coaxially within and extending longitudinally through said first-mentioned electrode, and a birefringent fluid within said container surrounding said electrodes.

9. In a circular polariscope including a condensing lens arranged adjacent either end of a light modulating cell, the combination with said lenses of a light modulating cell comprising an elongated hollow electrode positioned between said lenses with the axis of said electrode coincident with the focal axis of the lens, said electrode being provided with oppositely disposed substantially frustro-conical bores, the conical walls of which converge from the ends of the electrode towards a common plane of intersection located intermediate the ends of said electrode and substantially coincident with the focal point of said lenses, a second electrode arranged coaxially of said first-mentioned electrode, and means for immersing said electrodes in a body of hirefringent fluid.

10. A light modulating cell comprising a body of birefringent fluid, an elongated hollow electrode immersed in said fluid, a filament electrode extending coaxial within said hollow electrode in spaced relation with respect thereto, the space between said electrodes being occupied by said birefringement fluid, and means for passing a beam of light longitudinally through said hollow electrode.

11. A light modulating cell comprising means defining a path for a beam of light, an elongated electrode mounted coaxially of said light path, a second electrode surrounding the first-mentioned electrode and having a bore concentrically disposed with respect thereto, the inner walls of the second electrode converging from the opposite end thereof inwardly and longitudinally of the light path towards an intermediate portion of the electrode, and a birefringent medium completely surrounding said electrodes.

12. A light modulating cell comprising means defining a path for a beam of light, a filamentary electrode extending coaxially of the light path, a second electrode surrounding the first electrode and having a bore, the walls of said bore surrounding the first-mentioned electrode and being disposed concentrically with respect thereto, said walls diverging longitudinally of the light path from a position intermediate the ends of said first-mentioned electrode, and a birefringent medium surrounding both electrodes.

13. In a light modulating cell employing the Kerr effect, an electrode having a bore aligned with the light axis of the cell, a filamentary electrode positioned centrally of said bore in spaced relation to the inner surface thereof, a birefringent fluid surrounding at least the filamentary electrode, and means for producing a radial electrostatic field between said electrodes transversely of said light axis.

STEWART L. CLOTHIER. HAROLD C. HOGENCAMP. 

